Foot exerciser

ABSTRACT

A foot exercising device is disclosed. The foot exercising device includes a pair of foot pedals and a motor for reciprocating the foot pedals. A slip clutch is connected between the foot pedals and the motor to enable the foot pedals to be reciprocated independently of the motor. In the preferred embodiment, a control circuit controls the operation of the motor as a function of the number of reciprocations of the foot pedals and/or as a function of the blood flow through the patient using the foot exercising device.

RELATED APPLICATIONS

This is a divisional of U.S. patent application Ser. No. 85,330, filedOct. 29, 1979.

BACKGROUND OF THE INVENTION

The present invention is directed towards a foot exercising device, andmore particularly to a foot exercising device which is useful in theprevention of thrombosis of the legs. Devices of this general nature areknown in the prior art and exemplified by U.S. Pat. Nos. 3,526,220 and3,917,261.

Each year nearly 100,000 hospital patients die of pulmonary embolisms.These potentially lethal clots usually form in the leg veins and areoften caused by stagnation of blood circulation while the patient isimmobile following surgery or illness. Measures have been employed toprevent venous clotting in the legs including anti-coagulants,compression bandages, elastic stockings, leg elevation and earlyambulation. For a variety of reasons, none of these has proved to besatisfactorily effective. Patients exhibit a wide range ofsusceptibility to a standard anti-coagulant dose, which makes adequateprophylactic control difficult. Compression bandages and elasticstockings rarely maintain the necessary uniform compression on the legveins. Continued leg elevation is difficult to maintain for long periodsand imposes an additional load on the cardiovascular system which manypatients cannot tolerate. Ambulation often amounts to no more than a fewsteps around the bed once or twice a day.

There is persuasive clinical evidence that the best method forpreventing thromboembolism is to increase the speed of the blood flow inthe deep veins of the lower leg. Short of full ambulation (impossiblefor many post-operative and seriously ill patients), this increase invenous flow velocity is best accomplished by a regimen of leg exercisecarried out with adequate duration and frequency.

The purpose of leg exercising devices such as that described in theabove-noted patents, as well as that described herein, is toautomatically exercise the patient's legs so as to increase bloodcirculation in the area and thereby prevent the formation ofthromboemboli. The prior art foot exercising devices have recognizedthat it is desirable to run the exercisers in both a passive and anactive mode. In the passive mode of operation, the leg exercising devicemoves the patient's feet up and down through a predetermined arc for apreselected time period. In the active mode of operation, the patientsupplies the foot power himself against the resistive pressure which isselected by means of a brake pressure control knob.

BRIEF DESCRIPTION OF THE INVENTION

While the foregoing prior art foot exercising devices have beengenerally successful, the present invention includes many features whichresult in improved patient care. As noted above, the prior art footexercising devices operate in both a passive and an active mode. This ishighly desirable since it enables the patient to strengthen his legs byreciprocating the pedals on his own during the active mode and, at thesame time, ensures at least periodic movement of the patient's legs(during the passive mode of operation). The major drawback of the priorart devices is that the patient cannot pedal on his own during thepassive mode of operation. As such, the intervals during which thepatient can exercise his legs on his own is limited to the intervalsduring which the device is in the active mode of operation.

To overcome this drawback, the present invention utilizes a slip clutchor similar apparatus which permits the patient to disengage the motor,and thereby pedal on his own, during the passive mode of operation bymerely pedaling faster than the speed required by the motor. This samemechanism enables the patient to reciprocate the pedals on his ownduring the active mode of operation. As such, the present inventionprovides the patient with total freedom to exercise on his own wheneverhe finds it so desirable. At the same time, since the invention doesoperate in the passive mode of operation, the physician can be assuredthat the patient's legs will receive at least a minimal amount ofmovement.

In the above-noted prior art foot exercisers, the time duration duringthe passive and active modes of operation was controlled by apresettable timer. In the present invention, the active and passivemodes are not defined by preset time periods but by the number ofreciprocations of the pedals of the device. To this end, counters areprovided to count the pedal reciprocations during both the active andpassive modes of operation and to switch the device between these modesas a function thereof.

Yet another feature of the invention is the inclusion of controlcircuitry which varies the reciprocation frequency of the pedals of thefoot exerciser during the passive mode of operation as a function of thenumber of pedal reciprocations during the passive mode.

Yet another major feature of the present invention is the use of anon-invasive blood flow detector which generates an output signalindicative of the instantaneous blood flow through the patient's legs.This signal may be used to provide a visual display of the blood flowand/or to generate an alarm signal whenever the blood flow falls below apredetermined value. Finally, this signal may be used either to vary thereciprocation frequency of the pedals during the passive mode or toautomatically switch the foot exercising device into the passive modewhenever the blood flow through the legs of the patient falls below apredetermined value.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purpose of illustrating the invention, there is shown in thedrawings an embodiment which is presently preferred; it beingunderstood, however, that the invention is not limited to the precisearrangements and instrumentalities shown.

FIG. 1 is a perspective view of a foot exercising device constructed inaccordance with the principles of the present invention.

FIG. 2 is a block diagram of the foot exercising device of FIG. 1.

FIG. 3 is a first embodiment of the control circuit of FIG. 2.

FIG. 4 is a second embodiment of the control circuit of FIG. 2.

FIG. 5 is a block diagram of a second embodiment of a foot exercisingdevice constructed in accordance with the principles of the presentinvention.

FIG. 6 is a block diagram of the control circuit of FIG. 5.

FIG. 7 is a perspective view of a third embodiment of a foot exercisingdevice constructed in accordance with the principles of the presentinvention.

FIG. 8 is a block diagram of the embodiment of FIG. 7.

FIG. 9 is a block diagram of the control circuit of FIG. 8.

FIG. 10 is a block diagram of a possible modification of the controlcircuit of FIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, wherein like numerals indicate likeelements, there is shown in FIG. 1 a foot exercising device constructedin accordance with the principles of the present invention anddesignated generally as 10. A block diagram of the foot exercisingdevice of FIG. 1 is illustrated in FIG. 2.

As best viewed in FIG. 1, foot exercising device 10 includes a pair ofpedals 12, 14 which are pivotally connected to a housing 16 by anelongated shaft 18 extending between the opposite side walls of housing16. Reciprocating motion is imparted to pedals 12, 14 by a motor 20(preferably, but not necessarily, a variable speed motor) which islocated in housing 16 and whose speed is determined by a speed adjustswitch 26 which is coupled to housing 16. Speed adjust switch 26 mayinclude a rotary knob 27 coupled to the outside of housing 16 and avariable resistor whose rotary shaft is coupled for rotation therewith.More generally, speed adjust switch 26 may be any switch which willgenerate an output signal (normally an analog signal) indicative of thedesired speed of motor 20.

The output shaft (not shown) of motor 20 is coupled to pedals 12, 14 viaa slip clutch 22 and a cranking assembly 24 which serves to reciprocatepedals 12, 14 about shaft 18 responsive to the rotary motion of theoutput shaft of motor 20. While any suitable cranking assembly may beused, one acceptable assembly is described in U.S. Pat. No. 3,917,261.Cranking assembly 24 is preferably adjustable so as to permit the pedals12, 14 to be reciprocated out of phase with each other by any amountbetween 90°and 180°. It has been found that by adjusting the phase ofpedals 12, 14 to an intermediate setting of, for example, 120°, thepatient experiences a more pleasant sensation when using the device 10.

The use of slip clutch 22 enables the patient to override the drivingforce of motor 20 whenever he has sufficient energy to do so. This is anextremely desirable feature since it permits the physician to ensurethat the patient's legs will automatically be exercised and at the sametime permits the patient to strengthen his legs by overriding the motorand reciprocating pedals 12, 14 on his own. By way of example, thephysician may adjust the speed of variable speed motor 20 to run at arelatively slow speed which causes pedals 12, 14 to reciprocate at, forexample, 20 reciprocations per minute. The physician will then instructthe patient to pedal on his own whenever he possesses sufficientstrength to do so. The patient will do this by merely reciprocatingpedals 12, 14 at a reciprocation rate of greater than 20 reciprocationsper minute. In this connection, it should be noted that slip clutch 22will preferably slip only in one direction such that cranking assembly24 disengages from the output shaft (not shown) of motor 20 only whenpedals 12, 14 are reciprocated at a faster speed than that required bymotor 20.

While the speed of variable speed motor 20 is controlled by speed adjustswitch 26, the on-off state of motor 20 is controlled by control circuit28. More particularly, control circuit 28 turns on motor 20 responsiveto receipt of a start signal from a start switch 30 (or otherappropriate initiating mechanism) and maintains motor 20 in the oncondition until the pedals 12, 14 have reciprocated a preset number oftimes determined by preset count switch 32. As best seen in FIG. 1,preset count switch 32 is preferably coupled to the outside of housing16 and can take the form of a plurality of thumb wheel switches whichgenerate a digital output signal indicative of the desired number ofreciprocations during the passive mode of operation. This number may beadjusted by the physician or the patient by merely rotating the thumbwheel switches. While thumb wheel switches are illustrated, anyappropriate switch mechanism which can generate an output signalindicative of the desired number of reciprocations during the passivemode of operation may be used. After pedals 12, 14 have beenreciprocated the preset number of times, control circuit 28 turns offmotor 20.

In the event that the patient does not override motor 20 by pedalingfaster than the speed set by speed adjust switch 26, control circuit 28maintains foot exercising device 10 in the passive mode of operation fora time period determined by the speed of motor 20 and the preset count.If, however, the patient overrides the motor 20 by pedaling faster thanthe speed required by motor 20, the time duration during which footexercising device 10 remains in the passive mode will vary independentlyof the speed of motor 20 and the preset count. In either case, controlcircuit 28 turns motor 20 off after pedals 12, 14 have been reciprocatedthe predetermined number of times. When motor 20 is off, foot exercisingdevice 10 is in an active mode wherein the patient may reciprocatepedals 12, 14 on his own since slip clutch 22 permits pedals 12, 14 tobe reciprocated independently of motor 20. As such, foot exercisingdevice 10 switches between a single passive and a single active mode ofoperation.

It is sometimes desirable to ensure that the patient does not pedal thefoot exercising device subsequent to the passive mode of operation. Insuch a case, a locking devie 34 is added to the foot exercising device10. Locking device 34 is enabled by control circuit 28 whenever controlcircuit 28 shuts off motor 20 and prevents pedals 12, 14 fromreciprocating. By way of example, locking device 34 may be a frictionbrake which presses against pedals 12, 14 whenever motor 20 is off.Whenever the locking device 34 has been added to the foot exercisingdevice 10, device 10 operates only in a passive mode. The passive modemay, however, be overriden by the patient as a result of the presence ofslip clutch 22.

One suitable control circuit 28 for the embodiment of FIG. 2 isillustrated in FIG. 3. As shown therein, control circuit 32 includes areciprocation detector 36, a one shot 38, a counter 40 and a J-Kflip/flop 42. Reciprocation detector 36 monitors the movement of atleast one of the pedals 12, 14 and generates an output signal wheneverthe monitored pedal completes one full reciprocation. By way of example,but not limitation, reciprocation detector 36 may be a microswitchlocated in housing 16 in such a position that the microswitch is closedwhenever pedal 12 is in its lowermost position. Such a detection circuitwill generate a single output signal for each reciprocation of pedals12, 14.

The output of reciprocation detector 36 is applied to one shot 38 whichgenerates a single pulse (hereinafter count pulse) of predeterminedduration at its output responsive to each output signal generated byreciprocation detector 36. The count pulse generated by one shot 38 isapplied to the count input CT of counter 40 and causes the count incounter 40 to increase by 1 each time a new count pulse is appliedthereto. The count in counter 40 is initially set to 0 by the startpulse generated by start switch 30 (see FIG. 2). This signal is appliedboth to the clear input CL of count 40 and to the J input of J-Kflip/flop 42. In addition to setting the count in counter 40 to zero,the start pulse generated by start switch 30 sets flip/flop 42 causingits Q output to go to the binary "1" level. The Q output of flip/flop 42is applied to the on/off input of motor 20 which is turned on when the Qoutput of flip/flop 42 is at the binary "1" level.

Once foot exercising device 10 has been placed in the passive mode ofoperation by the start signal generated by start switch 30, counter 40continues to count the count pulses generated by one shot 38 until thecount in counter 40 reaches a preset count determined by the presetcount switch 32 (see FIG. 2). The digital signal generated by switch 32is applied to the preset input PST of counter 40. When the count incounter 40 reaches this preset level, it generates a single pulse on itscount full output CF which is applied to the K input of flip/flop 42.This causes flip/flop 42 to reset thereby switching the Q output offlip/flop 42 to the binary "0" level. As a result, motor 20 is turnedoff whenever counter 40 has counted the predetermined number ofreciprocations set by preset count switch 32.

A somewhat more sophisticated embodiment of control circuit 28 isillustrated in FIG. 4. To distinguish over the embodiment of FIG. 3,this circuit wil be identified as control circuit 28a. As noted above,control circuit 28 causes foot exercising device 10 to be cycled througha single passive and a single active mode. In order to reinitiate apassive mode of operation, the start switch 30 must again be depressed.In contrast, control circuit 28a illustrated in FIG. 4 continuallycycles foot exercising device 10 through several sequential passive andactive modes of operation. The particular duration of each of thesemodes is determined as a function of a preset reciprocation count forthe passive mode of operation and a second preset reciprocation countfor the active mode of operation. Since the slip clutch 22 permits thepatient to override the motor 20 in both the active and passive modes ofoperation, both of these modes are reciprocation dependent and timeindependent.

As shown in FIG. 4, the counter 40 of the embodiment of FIG. 3 isreplaced by separate passive mode and active mode counters 44, 46,respectively. Passive mode counter 44 counts the number ofreciprocations of pedals 12, 14 during the passive mode of operation bycounting the number of count pulses generated by one shot 38 during thismode. Active mode counter 48 counts the number of reciprocations ofpedals 12, 14 during the active mode of operation by counting the numberof count pulses generated during the active mode. The number ofreciprocations which are required during the passive mode of operationis determined by a preset count switch 48. The number of reciprocationsrequired during the active mode of operation is determined by a presetcount switch 50. Switches 48, 50 replace the single preset count switch32 of the foregoing embodiment. Accordingly, when utilizing the controlcircuit 28a of FIG. 4, the single preset count switch 32 illustrated inFIG. 1 is replaced by a pair of count switches. If desired, the twocount switches could be replaced by a single push-button keyboardcircuit and a pair of memories. The push-button keyboard circuit wouldbe used to enter the desired active and passive mode counts inrespective ones of the memories. The counts stored in each of thememories would be applied to respective preset inputs PST of memories44, 46.

Transfer between the passive and active modes of operation iseffectuated by J-K flip/flop 58 whose operation is controlled by thecount full outputs CF of counters 44, 46. When foot exercising device 10is first turned on, a start pulse is applied to the K input of J-Kflip/flops 52, 54 by start switch 30. As a result, both flip/flops 52,54 are reset causing their Q outputs to toggle to the binary "0" leveland causing their Q outputs to toggle to the binary "1" level. The Qoutput of flip/flop 54 is applied to the on/off input of motor 20 andturns motor 20 on (thereby placing foot exercising device 10 in thepassive mode). The binary "1" appearing at the Q output of flip/flop 52is applied to the enable input ENB of passive mode counter 44 therebyenabling counter 44. The binary "1" appearing at the Q output offlip/flop 52 is also applied to a one shot 56 which generates a singlepulse of predetermined duration each time the Q output of flip/flop 52transitions to the binary "1" level. As such, whenever flip/flop 52toggles to the reset state, the passive mode counter 44 is enabled, itscount reset to zero and the counter begins counting the count pulsesgenerated by one shot 38. Sinultaneously, active mode counter 46 isdisabled since the Q output of flip/flop 52 is at the binary "0" level.

Once the count in counter 44 has reached the preset number determined bypreset count switch 48, counter 44 generates a single pulse (an end ofpassive mode signal) on its count full output CF which is applied to theJ input of flip/flops 52, 54. This action sets both flip/flops. As aresult, the Q output of flip/flop 54 toggles to the binary "0" level,shutting off motor 20 and placing foot exercising device 10 in theactive mode of operation. Simultaneously, the Q and Q outputs offlip/flop 52 toggle to the binary "1" and binary "0" levels,respectively, thereby clearing and enabling active mode counter 46, anddisabling passive mode counter 44.

At this point, active mode counter 46 begins counting the count pulsesgenerated by one shot 38 and continues counting these pulses until thecount in counter 46 reaches the reset level determined by preset countswitch 50. At this time, active mode counter 46 generates a singleoutput pulse (an end of passive mode signal) at its count full output CFwhich is applied to the K input of flip/flops 52, 54. This action setsflip/flops 52, 54, thereby re-enabling motor 20 and passive mode counter44, disabling active mode counter 46, and repeating the above process.

In each of the foregoing embodiments of the invention, control circuits28, 28a only control the on/off condition of motor 20. In the embodimentof the invention illustrated in FIG. 5, control circuit 28' controls thespeed of motor 20 as well as the on/off condition thereof. In theembodiment described below, control circuit 28' operates motor 20 (andtherefore pedals 12, 14) at either one of two discrete speeds as afunction of the number of reciprocations of pedals 12, 14 during thepassive mode of operation. It should be recognized, however, that thecontrol circuit 28' can be used to adjust the speed of motor 20 in anydesired manner. For example, control circuit 28' can be used to adjustthe speed of variable speed motor 20 as a linear function of the numberof reciprocations of pedals 12, 14.

In the preferred embodiment, the operation of foot exercising device 10is initiated by depressing start switch 30 so as to generate a startpulse which is applied to control circuit 28'. In response to thispulse, control circuit 28' generates a signal on output line 60 whichcauses variable speed motor 20 to turn on. Simultaneously, controlcircuit 28' generates a signal on line 62 which sets the speed of motor20 to a first value corresponding to a preset pedal reciprocationfrequency, for example, 20 reciprocations per minute.

Control circuit 28' maintains this reciprocation frequency until it hasdetected a first predetermined number of pedal reciprocations, thisnumber being determined by first preset count switch 64. At this time,control circuit 28' changes the signal on line 62 to cause motor 20 tooperate at a second speed corresponding to a second pedal reciprocationfrequency (e.g., 30 reciprocations per minute). Finally, after controlcircuit 28' detects a second, higher, number of pedal reciprocations,this number being determined by a second preset count switch 66, controlcircuit 28' changes the signal on line 60 so as to shut off variablespeed motor 20 and place foot exercising device 10' in the active modeof operation.

One suitable control circuit 28' is illustrated in FIG. 6. As showntherein, control circuit 28' includes reciprocation detector 36, oneshot 38, counter 68, digital-to-analog (hereinafter D/A) converter 70and comparators 72, 74. As in the earlier embodiments, reciprocationdetector 36 and one shot 38 combine to generate a single count pulseapplied to the clock input CL of counter 68 responsive to eachreciprocation of pedals 12, 14. Counter 68 continually counts thesepulses and generates a binary signal on its count output CO indicativeof the instantaneous count in counter 68. In addition to receiving theclock pulses generated by one shot 38, counter 68 receives the startpulse generated by start switch 30 such that the count in counter 68 iscleared at the beginning of each passive mode of foot exercising device10'.

The count output CO of counter 68 is applied to D/A converter 70 whichconverts this signal to an analog signal and applies the convertedsignal to the inverting input terminal of comparators 72, 74. Comparator72 compares the instantaneous count in counter 68 with the preset countdetermined by first preset count switch 64 and controls the operation ofspeed adjust circuit 76 as a function thereof. Speed adjust circuit 76includes a transistor 78 and resistors R1 and R2 and applies either afirst predetermined voltage or a second predetermined voltage to thespeed control input of motor 20 as a function of the condition oftransistor 78. Particularly, when transistor 78 is on, the voltage V1appearing at its emitter is applied to the speed control input of motor20 via line 60. When transistor 78 is off, a second voltage, determinedby the magnitude of voltage V2 and the voltage divider R1-R2, is appliedto the speed control input of motor 20 via line 60.

As long as the count in counter 68 remains below the predetermined countset by said preset count switch 64, the output of comparator 72 will beat the binary "0" level and transistor 78 will be turned on. In thiscondition, the voltage V1 will be applied to the speed control of motor20. As soon as the count in counter 68 rises above the level determinedby preset count switch 64, the output of comparator 72 will switch tothe binary "1" level turning transistor 78 off. In this condition, thevoltage applied to the speed control input of motor 20 will change tothe value determined by voltage V2 and voltage divider R1-R2. Ifvoltages V1 and V2 are kept constant, foot exercising device 10' will becapable of operating at only two discrete speeds. For this reason, it isusually desirable to provide means for varying the voltages V1, V2 so asto enable the physician to select the two desired motor speeds, andtherefore the two pedal reciprocation frequencies, in accordance withthe needs of the patient. A similar result may be obtained by replacingeither resistor R1, R2 with an appropriate potentiometer.

As noted above, the output of D/A converter 70 is also applied to theinverting input terminal of comparator 74. Comparator 74 controls theon/off condition of motor 20. To this end, comparator 74 compares thecount in counter 68 to the preset count determined by second presetcount switch 66. As long as the count in counter 68 remains below thiscount, comparator 70 will generate a binary "1" on its output. Thissignal is applied to the on/off control input of motor 20 via line 62and turns the motor 20 on. The output of comparator 74 remains at thislevel until the count in counter 68 reaches the preset level determinedby second preset count switch 66 at which time the output of comparator74 toggles to the binary "0" level and motor 20 is turned off.

A third embodiment of the exercising device 10" of the present inventionis illustrated in FIG. 7. In this embodiment, a non-invasive blood flowdetector 80 is coupled to the housing 16 of foot exercising device 10"by an electrical line 82. The non-invasive blood flow detector 80 isadapted to be placed around the leg of the patient and detects the bloodflow in the patient's leg. Detector 80 generates an output signal online 82 indicative of the blood flow in the patient's leg. While anyappropriate blood flow detector 80 may be used, one suitable detector isa sonic detector manufactured by Metrix-Technics under the productdesignation Pulsed Doppler Ultransonic Flow Detector.

The electrical line 82 is connected to a display unit 84 is preferably,but not necessarily, located at the top of housing 16. Display unit 84provides the patient and/or the physician with a visual indication ofthe rate of blood flow through the patient's leg. This information isextremely important, since it will enable the physician to select boththe pedal reciprocation frequency and the number of reciprocationsduring the passive mode of operation in a manner which is tailored tothe specific needs of the patient being treated. It will also enable thepatient to visually see that he is being helped by exercising device10".

As noted above, the primary purpose of foot exercising device 10" is toprevent the formation of blood clots in the patient's legs. To this end,it is necessary to ensure that the blood flow through the patient's legsremains above some predetermined minimum value. In the preferredembodiment of the present invention, the display unit 84 includes anaudible and/or visual alarm which is activated whenever the patient'sblood flow falls below the predetermined level. Such an alarm may beformed by merely using a comparator circuit which compares the signal inline 82 (representative of the actual blood flow through the patient'slegs) with a second signal (preferably adjustable by the physician)indicative of the minimum acceptable rate of blood flow. Whenever theactual blood flow falls below the minimum blood flow level, thecomparator generates an output signal which can be applied to an audiblealarm circuit.

In the embodiment illustrated in FIG. 7, both the display unit 84 andthe alarm housed therein are connected to the housing 18. It is oftendesirable to locate both the display unit 84 and the associated alarmcircuit at some central location such as the nurse's desk in a hospitalward. In such a case, the blood flow information generated by detector80 will be transmitted to the central location either through cables orusing radiowaves. If several foot exercising devices 10" are used in thesame ward, the signals from each of the different exercising devices 10"may all be transmitted to the central location where they are displayedon associated displays 84. In the event that the blood flow through anyof the patients' legs falls below the minimum acceptable value, an alarmsignal will be generated at the central location indicating whichpatient is in danger.

In the embodiment of FIG. 7, the blood flow information is used merelyfor the purpose of displaying the instantaneous blood flow through thepatient's legs and for generating an alarm signal whenever the bloodflow falls below a predetermined minimum value. It is possible, however,to use the blood flow information as an additional control input forcontrolling the operation of foot exercising device 10". A block diagramfor such a device is illustrated in FIG. 8. This block diagram isidentical to that of FIG. 2 with the addition of blood flow detector 80and display and/or alarm circuit 84. The control circuit 28" may takethe form of any of the control circuits illustrated in FIGS. 3, 4 or 6or any other desirable variation thereon) with the addition of thecircuitry illustrated in FIG. 9. In this Figure, the block identified ascounter circuit 86 represents the control cirucit of the foregoingembodiments. By way of example, if the embodiment of FIG. 3 is utilized,counter circuit 86 includes elements 36-42. In such a case, countercircuit 86 would include a single output line (shown in solid lines)which is coupled to one input of OR-gate 88. If the control circuit ofFIG. 6 is utilized, counter circuit 86 includes elements 36, 38 and68-78. In such a case, counter circuit 86 includes both an on/off and aspeed output. The on/off output is represented in solid lines andapplied to one input of OR-gate 88 while the speed output is shown indashed lines and would be applied to the speed control of motor 20 (inlieu of speed adjust switch 26).

In addition to counter circuit 86, control circuit 28" includes acomparator 90 and a preset switch 92. The preset switch is preferablyadjustable by the physician and generates an output signal indicative ofthe minimum acceptable blood flow through the patient's legs. Thissignal is compared in comparator 90 to the output of blood flow detector68. As long as the blood flow through the patient remains above thepredetermined level set by preset switch 92, the output of comparator 90will be a binary "0" and the on/off operation of motor 20 will becontrolled by counter circuit 86 (i.e. as a function of the number ofreciprocations of pedals 12, 14). If, at any time, the actual blood flowthrough the patient's legs falls below the preset value determined bypreset switch 92, comparator 90 generates a binary "1" on its output andapplies this signal to the on/off control of motor 20 via OR-gate 88. Asa result, motor 20 will be turned on whenever the blood flow through thepatient's legs falls below the predetermined minimum value. This ishighly desirable since it ensures that the patient's legs will beexercised whenever his blood flow reaches a critical stage irrespectiveof the number of prior reciprocations of pedals 12, 14. While it isusually desirable to control the operation of motor 20 both as afunction of the number of pedal reciprocations and the rate of bloodflow through the patient's legs, it is sometimes desirable to controlthe operation of motor 20 solely as a function of the blood flow throughthe patient's legs. For example, it may be desirable to enable motor 20,and thereby place foot exercising device 10" in a passive mode, wheneverthe blood flow through the patient falls below a predetermined level. Insuch cases, a bypass switch 94 (shown in phantom) may be added tocontrol circuit 28". Whenever it is desirable to control the operationof foot exercising device 10 solely as a function of the flow of bloodthrough the patient, switch 94 is closed, thereby short-circuitingOR-gate 88 and connecting the output of comparator 90 directly to theon/off control of motor 20.

In the foregoing embodiment, the rate of blood flow through thepatient's legs is used merely to control the on/off condition of motor20. The speed of motor 20 may, however, also be controlled as a functionof blood flow. In such a case, circuitry could be included to vary thespeed of motor 20 as a linear or discrete function of the instantaneousblood flow through the patient. One example of a control circuit whichvaries the speed of motor 20 as a discrete function of blood flow isillustrated in FIG. 10. This circuitry is substantially identical to thespeed control circuitry of FIG. 6 except that the output of blood flowdetector 80, rather than the output of D/A converter 70, is applied tothe inverting input terminal of comparator 72. Additionally, comparator72 compares the output of blood flow detector 80 to a blood flow signalgenerated by a preset switch 96 which is adjustable by the physician andwhich indicates the blood flow level at which the reciprocatingfrequency is to change. Since the operation of speed adjust circuit 76is otherwise identical to that described with reference to FIG. 6 above,an additional description of this circuit will not be set forth herein.The circuitry of FIG. 10 may be utilized either in lieu of or inconnection with the circuitry of FIG. 9.

The present invention may be embodied in other specific forms withoutdeparting from the spirit or essential attributes thereof and,accordingly, reference should be made to the appended claims, ratherthan to the foregoing specification as indicating the scope of theinvention.

What is claimed is:
 1. A foot exercising device, comprising:a pair offoot pedals; motor means for reciprocating said foot pedals; and controlcircuit means for controlling the operation of said motor means, saidcontrol circuit means counting the number of reciprocations of saidpedals and varying the speed of said motor means as a function of saidcount.
 2. The foot exercising device of claim 1, wherein said controlcircuit means enables said motor means during a passive mode ofoperation and disables said motor means during an active mode ofoperation.
 3. The foot exercising device of claim 2, wherein saidcontrol circuit means includes:means for generating a count pulse eachtime said pedals complete a single reciprocation; means for countingsaid count pulses during said active mode of operation; and means forcausing said motor means to vary said reciprocation frequency of saidpedals as a function of the number of pulses counted by said countingmeans.
 4. The foot exercising device of claim 3, wherein said speedvarying means:causes said motor means to reciprocate said pedals at afirst frequency when the number of pulses counted by said counter meansis less than a first number; causes said motor means to reciprocate saidpedals at a second frequency when the number of pulses counted by saidcounter means is greater than said first number but less than a second,greater number; and disables said motor means, and thereby places saidmotor means in said active mode, when said number of pulses counted bysaid counter means is greater than or equal to said second number. 5.The foot exercising device of claim 4, further including means foradjusting said first and second numbers.
 6. The foot exercising deviceof claim 5, further including means for adjusting the value of saidfirst and second frequencies.